Trypanosomatids are parasites that cause debilitating and often fatal diseases in humans and livestock. A particularly serious problem in sub-Saharan Africa is caused by Trypanosoma brucei, a parasite spread by the bite of an infected Tsetse fly. T. brucei causes disease by proliferating in the blood, tissue spaces, and eventually the central nervous system of its mammalian host. Related parasites are equally important to human populations in other parts of the world, including South and Central America, Southeastern Asia and the Middle East. Our long-term goal is to understand, in biochemical and genetic detail, the mechanisms that coordinate gene expression in trypanosomatids. To achieve this goal, we are specifically investigating the mechanism used by the parasites to regulate their mRNA expression pattern. mRNA expression gives rise to a characteristic and essential proteome and determines the metabolic capabilities of the parasites. As a pathway into understanding mRNA expression control, we are studying a novel RNA-binding protein, RBP42, which was chosen for investigation because it (1) is essential for parasite proliferation and (2) binds to the coding region (open reading frame) of mRNAs encoding a variety of enzymes and proteins within the cells' energy metabolic pathways. We currently know of no other trypanosome protein with this binding specificity; however there is an increasing awareness of coding region binding proteins in the fields of neurobiology and development. Furthermore, our data suggest that RBP42 is an important factor in mRNA translation, mRNA stability or mRNA sequestration as it binds to polysome-associated, translating mRNAs during the procyclic stage of the T. brucei life-cycle. In our aim, we will explore the function of RBP42 by determining its role and mode of action in gene expression networks of T. brucei. This exploratory, two-year project is grounded in preliminary data, in a recent publication from our laboratory, preliminary data and complementary in vivo molecular genetic and in vitro biochemical approaches.